Phialophora gregata, the brown stem rot pathogen, appears to survive solely in soybean residue. Therefore, decomposition of residue is believed to be an important factor in managing this pathogen. Tilling soil increases decomposition of residue and will affect how much brown stem rot fungus survives from year to year. We have observed greater severity of BSR and lower yields in soybean grown under no-till, especially if shorter rotations are used (Table 1).

*The severity of brown stem rot measured on a scale of 0 (none) to 11 (100% of leaves had symptoms). Data represent the means of eight location years from 1989-1992 at Arlington, WI.

Current studies indicate that the greater disease severity associated with no-till systems is related to higher inoculum density of the BSR pathogen within soybean residue (Figure 1) and a slowed decomposition of soybean residue when the residue is left on or above the soil surface. This combination of factors results in higher inoculum levels of the pathogen over a longer period of time. However, our no-till plots are relatively new. The long term effects of a not-till system on soybean health and productivity are yet to be determined.

We support the adoption of no-till systems, but encourage farmers who use this system to carefully monitor their fields for changes in the severity of brown stem rot. Longer crop rotations and shredding soybean straw with a combine-mounted shredder are effective practices that can be used to supplement resistant varieties in reducing the risk of brown stem rot in no-till systems. It is critical to implement crop scouting for early detection of pathogen build-up. Although fungicide seed treatment will not control BSR, it is a sound practice to treat seed with a fungicide if no-till and early planting are part of the management system.

Figure 2. The inoculum level of Phialophora gregata was determined in soybean residue placed on the soil surface or buried. Inoculum level is expressed as the amount of pathogen detected per square meter. Means designated by different letters are significantly different (P=0.10)